Page 1103 - Veterinary Immunology, 10th Edition

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reaction is characterized by infiltration with γ/δ , CD4 , and CD8 T
VetBooks.ir cells. This is a very convenient and rapid method of assessing an
animal's ability to mount a cell-mediated response without the need
for first sensitizing the animal to an antigen. However, the response

to phytohemagglutinin is nonspecific, and its interpretation may be
difficult.

In Vitro Techniques

In vitro tests are designed to measure the antigen-specific activation
and proliferation of T cells. These also include their cytotoxic
activities and their production of cytokines. All of these tests
require that T cells be grown in cell culture; therefore, few are
useful for use in the field.

To measure T cell proliferation in response to an antigen, a
suspension of purified peripheral blood lymphocytes from the
animal to be tested is mixed with the antigen and cultured for 48 to

96 hours (Fig. 33.8). Twelve hours before harvesting, thymidine
labeled with the radioactive isotope tritium is added to the cultures.
Normal, nondividing lymphocytes do not take up thymidine, but
dividing cells that are actively synthesizing DNA do. Thus if the T
cells are proliferating, they will take up the tritiated thymidine.

Their radioactivity will provide a measure of this proliferation. The
greater their proliferation in response of the cells to an antigen, the
greater will be their radioactivity. The ratio of the radioactivity in

the stimulated cultures to the radioactivity in the controls is called
the stimulation index. A related technique is to measure the
proliferation of lymphocytes in response to mitogenic lectins such
as concanavalin A (see Box 13.2). The intensity of the lymphocyte
proliferative response, as measured by tritiated thymidine uptake,

provides an estimate of the reactivity of an animal's lymphocytes.

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